A review on clay chemistry, characterization and shale inhibitors for water-based drilling fluids

Challenges associated with drilling operations are numerous and their adverse effect could lead to severe damage or even shutting down of the drilling operations. Wellbore instability among others is but the most encountered problem by drilling engineers when water-based drilling fluids (WBDF) are applied. This is because shale formations are full of active clay minerals which can lead to hydration and swelling once encountered by the WBDFs thus destabilizing the integrity of the wellbore. To combat this, most petroleum engineers have employed different inhibitors to reduce or stop the menace posed by these active clay minerals. The purpose of this study is to highlight in detail the essential types of clays mostly encountered in drilling operations, the swelling mechanism of the active clay minerals, comprehensive characterization techniques, and the differences associated with the applied inhibitors reported in the literature for tackling clay hydration and swelling. Based on the review, we recommend extensive evaluation between smectite and vermiculite clay minerals during analysis to determine the effectiveness of some of the characterization techniques adopted for the inhibition studies. Also, a methodology blueprint for specific clay mineral types is highly recommended for future researchers to help reduce the uncertainty associated with the reported outcomes of these active clay minerals. At least five characterization techniques such as linear swelling test (LST), scanning electron microscopy (SEM), x-ray diffraction (XRD), bulk hardness test (BHT), and wettability alteration test (WAT) to be conducted for any experimental procedure to be able to understand in detail the inhibitive mechanism of the applied inhibitors. Environmentally friendly inhibitors that are cheap, pollution-free with excellent stability in harsh environments are highly encouraged since they can be sustained and have good inhibition potential.